Agriculture is a priority sector in Saudi Arabia. During last three decades, the country achieved significant growth in agricultural production. Despite difficulties of scarce rain, meager subterranean water, limited local manpower and widely dispersed cultivatable lands, agriculture has been given priority with objectives of attaining self-sufficiency, enhancing food security and increasing rural income. Agricultural productivity heavily relies on spatial and temporal variation of climate parameters like temperature, rainfall and humidity. Crop production is particularly vulnerable to variations in temperature and water availability during grain maturing stage. This paper presents the result of research work on effects of fluctuations in maximum and minimum temperature, water availability and humidity at different stages of plant growth for few major crops of the country which include wheat, date, and vegetables. Parametric analysis is conducted using historical climate data integrated into crop production simulation model to assess relative impacts of variations of climate parameters. PRECIS model is used for predictions of future climate parameters up to the end of the century. Climate forecasts are fed into DSSAT crop production simulation model to investigate corresponding impacts. Results suggest that yield of wheat, barley, date and vegetables may reduce by more than 30 percent due to change of temperature and rainfall forecasted in SRES scenarios. Outputs of analysis may be utilized for climate change adaptation policy formulation.